Ganglioside is the generic term for glycosphingolipids containing sialic acids, which are an amphiphilic molecular species consisting of a hydrophilic saccharide moiety and a hydrophobic ceramide moiety. They are ubiquitous constituents of mammalian cells.
Gangliosides play a fundamental role as an acceptor for a number of biological ligands such as various cytotoxins (cholera vibrio, tetanus bacillus, Clostridium botulinum, Vibrio parahaemolyticus, Staphylococcus, etc.), hormones (thyrotrophic hormone, luteinizing hormone), interferons, neurotransmitters (serotonin, noradrenalin, dopamine, histamine) and influenza viruses.
On the surface of influenza virus membrane occur hemagglutinin [W. Weis et al., Nature, Vol. 333, 426 (1988)] and neuraminidase [P. M. Colman et al., Nature, Vol. 303, 41 (1983)], the former specifically recognizing sialic acid-containing saccharide chains. They play an important role in adsorption on and invasion into animal cells of influenza viruses, which are important constituents in the mechanism of the adsorption and invasion when viewed from the host with respect to prevention of viral infection.
We have investigated the effects of various ganglioside analogs on activity of influenza virus neuraminidases with interesting results [Y. Suzuki et al., Glycoconjugate J., 7 (1990)].
Such substances strongly binding to influenza virus neuraminidases but not a substrate for the enzymes may be very useful for the analysis of the three-dimensional structure of activity center of the enzyme, leading to an approach for prevention of viral infections.
Partial acetylation of sialic acids may protect them against the action of sialidases, and may also influence the antigenicity of human melanoma cells and of bacterial polysaccharides. It has also been reported that the acetylatoin of sialic acids can be necessary for the binding of viruses [Y. Suzuki, TRENDS IN GLYCOSCIENCE AND GLYCOTECHNOLOGY, Vol. 2, 4, 112 (1990)].
Sialic acid is a generic term for a member of neuraminic acid derivatives, which contains acetyl and glycolyl groups as substituent on the amino group and acetyl, lactyl, phosphate, sulfate, methyl or other groups as substituent on the hydroxyl groups. Presently, approximately 30 species of sialic acid have occurred and determined for structure.
As principal functions of sialic acids are mentioned, for example, (1) providing glycoconjugates and cell membranes with negative charge, (2) influence upon the conformation of glycolipids or glycoproteins, (3) information transmission and (4) masking action on the antigenic site [R. Shauer, T.I.B.S., 10, 357 (1985)]. Role of sialic acids will attract increasing interests in the future.
As described above, gangliosides take part in a variety of biological phenomena. A constituent of the gangliosides, sialic acids are considered to have a great influence upon the occurrence of the activities.
In order to elucidate the effects of the structure of sialic acids upon the occurrence of the activities of gangliosides it is necessary to prepare a variety of gangliosides containing a chemically modified sialic acid. Elucidation of the function of gangliosides on a molecular level would be accomplished using such modified compounds.